The researchers reviewed 28 studies on almost 100,000 people looking at vitamin D levels among middle-aged and elderly people; they examined the effect of the vitamin on cardiovascular disease, Type 2 diabetes and metabolic syndrome.

One of the study authors, Dr Johanna Parker, who works in a Birmingham GP practice, said: “The research we conducted looked at naturally occurring vitamin D rather than supplements.

"We recommend people eat a healthy diet with two to three portions of oily fish a week and five portions of fruit and vegetables.